بررسي آزمايشگاهي و آماري بهسازي يك خاك متورم شونده با استفاده از الياف مصنوعي و افزودني‏هاي شيميايي

Experimental and statistical assessment of expansive soil treatment using artificial fiber and chemical stabilizer

در اين پژوهش يك برنامه آزمايشگاهي براي بهسازي و كاهش پتانسيل تورمي يك خاك متورم شونده رسي به روش مكانيكي (مسلح‏سازي) و شيميايي در نظر گرفته شد. در روش مكانيكي از دو نوع الياف مصنوعي از نوع ميله‏اي و نواري و به ترتيب از جنس پلي‏اتيلن و پلي‏پروپيلن با درصد‏هاي وزني و طول‏هاي گوناگون استفاده شد. همچنين بهسازي خاك به روش شيميايي با استفاده از آهك و سيمان با درصد‏هاي وزني و زمان‏هاي عمل‌آوري متفاوت صورت پذيرفت. علاوه بر آن نتايج آزمايشگاهي مورد تجزيه و تحليل آماري قرار گرفت و مدل‏هاي رگرسيوني چندگانه مناسب براي پيش‏بيني و تعيين منحني تورم آزاد، درصد تورم آزاد نهايي و فشار تورمي و بررسي ارتباط و همبستگي بين پارامترهاي موثر در پديده تورم به صورت تابعي از درصد وزني الياف، نسبت طول به قطر يا عرض الياف، درصد وزني آهك يا سيمان و زمان عمل آوري با دقت مطلوب پيشنهاد شد. نتايج به دست آمده نشان داد كه بهسازي خاك با استفاده از الياف مصنوعي و افزودني‏هاي شيميايي موجب كاهش قابل توجه در پتانسيل تورمي خاك متورم شونده مي‌شود، به طوري كه سيمان، آهك، الياف نواري و ميله‏اي به ترتيب بيشترين تاثير در كاهش پتانسيل تورمي را دارد

Expansive soils are found in many parts of the world particularly in arid and semi-arid regions. They are considered a worldwide problem as they cause extensive damage to civil engineering structures. As a result, a clear understanding of the behavior of such soils is required for the effective design of structures and infrastructures on these soils. Researchers have demonstrated various methods to reduce expansive soils swelling potential, with one being soil treatment. In this paper an experimental program was developed to study the treatment of an expansive soil using mechanical and chemical techniques. Two different types of artificial fiber consisting of polyethylene (bar shaped) with a diameter of 0.3 mm and polypropylene (tape shaped) with a width of 3 mm were used in order to randomly reinforce soil samples with various fiber contents of 0.5 %, 1 % and 1.5 %; and fiber lengths of 10, 20 and 30 mm. Chemical treatment was carried on using lime and cement as soil stabilizers with various percentages of 5 %, 8 % and 10 %; for curing times of immediate, 3 and 7 days. A total of 37 (36 treated and 1 untreated) uniform and repeatable moist-compacted soil samples were prepared by static compaction at a chosen moisture content and dry density less than the optimum water content and maximum dry density from standard proctor compaction tests. Free swelling and swelling pressure tests were conducted using a one-dimensional oedometer apparatus in order to determine swelling potential of various treated soil samples. In addition multiple regression equations with 3 and 2 independent variables were developed based on experimental results. The proposed multiple regression equations present an understanding of the variation of free swelling and swelling pressure as a function of swelling time, fiber or chemical stabilizer content and fiber aspect ratio (fiber length divided to fibers diameter or width) or curing time for various values. Experimental results and statistical analysis indicated that soil treatment with artificial fibers and chemical stabilizers can indeed reduce swelling potential in expansive soils. Reduction of free swelling and swelling pressure in samples randomly reinforced with artificial fiber was seen to be dependent on fiber content, fiber length and fiber shape, where tape shaped fibers showed more reduction in free swelling and swelling pressure thus being more effective compare to bar shaped fibers. Furthermore reduction of free swelling in samples treated with chemical stabilizers were seen to be a function of percentage of chemical stabilizer and curing time with cement showing to be more effective compare to lime. In addition chemical stabilizers proved to be more effective in reducing soils swelling potential compare to artificial fibers. The suggested regression equations can predict and estimate the free swelling curve, final free swelling and swelling pressure for various swelling time, fiber or chemical stabilizer content and fiber aspect ratio or chemical stabilizer curing time with accuracy and a high degree of agreement between experimental and predicted values. Also, the regression equations can aid the performance of a sensitivity analysis which indicates the importance of each independent variable (fiber or chemical stabilizer content, fiber aspect ratio or chemical stabilizer curing time) in estimating final free swelling and swelling pressure.